Weighting and Expanding Query Terms Based on Language Model Favoring Surprising Words

ABSTRACT

An approach is provided that receives a question at a question answering (QA) system. The question includes a number of words. The approach operates by calculating weights that correspond to search terms included in the plurality of words. The search terms include the plurality of words and may include terms that are one or more sequences of adjacent words included in the question. Based on the calculated weights and the words in the question, the approach generates a query that is used to search a corpus that is managed by the QA system with the search resulting in one or more search results.

BACKGROUND OF THE INVENTION Description of Related Art

A challenge in Question Answering (QA) systems is that relevant passagesand documents with the correct answer from an open domain query are notalways returned with a high rank. The goal is to improve the querygeneration step in formulating the query for a search for open domainquestion answer systems. Traditional QA systems formulate a query basedon the terms in the question, after performing operations like droppingcommon stop words (such as “the,” “in,” etc.), weighting (boosting)certain terms, deciding whether search terms are mandatory or optional,and performing an expansion on terms to automatically include relatedterms, such as synonyms, etc. There is an art to query formulation, assometimes trying to expand queries, by including synonyms for example,can generate noise in the returned passages and result in less usefulpassages being returned by the QA system. Sometimes terms are dropped,because they are very common, in cases where they should have beenincluded in the search because such terms are a key idea in the search(such as the word “not,” which is sometimes dropped from search terms).A challenge in QA system development, therefore, is to improve queryformulation by selectively boosting and expanding certain terms withoutadding undue noise by including too many search terms.

SUMMARY

An approach is provided that receives a question at a question answering(QA) system. The question includes a number of words. The approachoperates by calculating weights that correspond to search terms includedin the plurality of words. The search terms include the plurality ofwords and may include terms that are one or more sequences of adjacentwords included in the question. Based on the calculated weights and thewords in the question, the approach generates a query that is used tosearch a corpus that is managed by the QA system with the searchresulting in one or more search results.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations, and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, inventive features, and advantages of the present inventionwill be apparent in the non-limiting detailed description set forthbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings, wherein:

FIG. 1 depicts a network environment that includes a knowledge managerthat utilizes a knowledge base;

FIG. 2 is a block diagram of a processor and components of aninformation handling system such as those shown in FIG. 1;

FIG. 3 is a high level diagram that depicts enhanced weighting andinclusion of search terms;

FIG. 4 is a diagram showing a first example of a comparison of weightedquery terms using traditional weighting and inclusion of search termsand query terms boosted with enhanced weighting and inclusion of searchterms;

FIG. 5 is a diagram showing a second example of a comparison of weightedquery terms using traditional weighting and inclusion of search termsand query terms boosted with enhanced weighting and inclusion of searchterms;

FIG. 6 is a depiction of a search weight calculation of terms includedin a third example question posed to a QA system using enhancedweighting and inclusion of search terms;

FIG. 7 is a depiction of a flowchart showing the logic used to computeenhanced weighting and inclusion of search terms for a given search; and

FIG. 8 is a depiction of a flowchart showing the logic used to expandsearch terms used in query based on enhanced weighting and inclusion ofsearch terms.

DETAILED DESCRIPTION

FIGS. 1-8 describe an approach that provides weights of search termsthat are used when searching a corpus managed by a question answering(QA) system. A statistical language model is a probability distributionof sequences of words. This approach uses a formula, based on the loglikelihood statistics (a derivative of the probability) from a languagemodel generated for the corpus from Unigrams, Bigrams. n-grams forwords. (in one embodiment, the approach utilizes the Berkeley Languagemodel). Below is the method we are using to determine the term weightsfor this invention, and rules for applying those weights to decide stopwords and mandatory terms.

The approach processes n-gram models using the following algorithm,where W=the weight of the term, n=the number of grams, α_(i)=constantvalue for gram (i), and L_(i)=the likelihood of the term (likelihood ofsingle word for unigram, two adjacent words for bigram, etc.).

$W = {\sum\limits_{i = 1}^{n}\; {\alpha_{i}*{{abs}\left( L_{i} \right)}}}$

For any given corpus, the constants to use can be determined by trainingnd testing based on the documents in the corpus (document database). Twothresholds are used (t₁ and t₂) so that if a term exceeds (is greaterthan) the first threshold (t₁) then the approach ensures that the termis not removed by a stop list (e.g., list of words commonly removed froma search, etc.). If the term exceeds the second threshold (t₂), then theapproach ensures that the term is included as a mandatory term in thesearch.

The idea behind this approach is if unlikely words are included in aquestion (relative to works preceding them), they may be particularrelevant and boosted in a variety of ways. The weights are calculatedusing the formula above based on log likelihood. These weights are addedto the Lucene query.

For example, consider the open language query: “Who did Pakistan'sSupreme Court acquit of hijacking charges dating from an 1999 armycoup?”

In traditional QA systems, the document query that would result from theexample question might appear as:

-   -   “+contents:armi+contents:charg+contents:coup+contents:pakistan+contents:1999+contents:suprem+contents:court        contents:did contents:acquit contents:hijack contents:date        contents:from spanNear([contents:did, contents:pakistan], 2,        false)̂0.4 spanNear([contents:pakistan, span        Near([contents:suprem, contents:court], 2, true)], 2, false)̂0.4        spanNear([spanNear([contents:suprem, contents:court], 2, true),        contents:acquit], 2, false)̂0.4 spanNear([contents:acquit,        contents:hijack], 2, false)̂0.4 spanNear([contents:hijack,        contents:charg], 2, false)̂0.4 spanNear([contents:charg,        contents:date], 2, false)̂0.4 spanNear([contents:date,        contents:from], 2, false)̂0.4 spanNear([contents:from,        contents:1999], 2, false)̂0.4 spanNear([contents:1999,        contents:armi], 2, false)̂0.4 spanNear([contents:armi,        contents:coup], 2, false)̂0.4

And the resulting passage query in a traditional QA system might appearas:

-   -   contents:pakistan contents:suprem contents:court contents:did        contents:acquit contents:hijack contents:charg contents:date        contents:from contents:1999 contents:arm i contents:coup        spanNear([contents:did, contents:pakistan], 2, false)̂0.4        spanNear([contents:pakistan, span Near([contents:suprem,        contents:court], 2, true)], 2, false)̂0.4        spanNear([spanNear([contents:suprem, contents:court], 2, true),        contents:acquit], 2, false)̂0.4 spanNear([contents:acquit,        contents:hijack], 2, false)̂0.4 spanNear([contents:hijack,        contents:charg], 2, false)̂0.4 spanNear([contents:charg,        contents:date], 2, false)̂0.4 spanNear([contents:date,        contents:from], 2, false)̂0.4 spanNear([contents:from,        contents:1999], 2, false)̂0.4 spanNear([contents:1999,        contents:armi], 2, false)̂0.4 spanNear([contents:armi,        contents:coup], 2, false)̂0.4 using passage search method:        CONTEXT

Using the approach described herein, the document and passage queriesare shown with weightings that reflect the surprise nature of one ormore of the search terms, with noted weightings highlighted in boldbelow:

Document query using approach described herein:

-   -   +contents:armî1.8219616+contents:charĝ1.5046515+contents:coup̂2.0959115+contents:pakistan̂2.1257643+contents:1999̂2.6136165+contents:suprem̂1.8141896+contents:court̂1.7127338        contents:did̂1.9036298 contents:acquit̂2.4188824        contents:hijack̂2.9932864 contents:datê2.2353313        contents:from̂1.0671548 spanNear([contents:did, contents:        pakistan], 2, false)̂0.4 spanNear([contents:pakistan, span        Near([contents:suprem, contents:court], 2, true)], 2, false)̂0.4        spanNear([spanNear([contents:suprem, contents:court], 2, true),        contents:acquit], 2, false)̂0.4 spanNear([contents:acquit,        contents:hijack], 2, false)̂0.4 spanNear([contents:hijack,        contents:charg], 2, false)̂0.4 spanNear([contents:charg,        contents:date], 2, false)̂0.4 spanNear([contents:date,        contents:from], 2, false)̂0.4 spanNear([contents:from,        contents:1999], 2, false)̂0.4 spanNear([contents:1999,        contents:armi], 2, false)̂0.4 spanNear([contents:armi,        contents:coup], 2, false)̂0.4

Passage query using approach described herein:

-   -   contents: pakistan̂2.1257643 contents:suprem” 1.8141896        contents:court̂1.7127338 contents:did̂1.9036298        contents:acquit̂2.4188824 contents:hijack̂2.9932864        contents:charĝ1.5046515 contents:datê2.2353313        contents:from̂1.0671548 contents:1999̂2.6136165        contents:armî1.8219616 contents:coup̂2.0959115        spanNear([contents:did, contents:pakistan], 2, false)̂0.4        spanNear([contents:pakistan, spanNear([contents:suprem,        contents:court], 2, true)], 2, false)̂0.4        spanNear([spanNear([contents:suprem, contents:court], 2, true),        contents:acquit], 2, false)̂0.4 spanNear([contents:acquit,        contents:hijack], 2, false)̂0.4 spanNear([contents:hijack,        contents:charg], 2, false)̂0.4 spanNear([contents:charg,        contents:date], 2, false)̂0.4 spanNear([contents:date,        contents:from], 2, false)̂0.4 spanNear([contents:from,        contents:1999], 2, false)̂0.4 spanNear([contents:1999,        contents:armi], 2, false)̂0.4 spanNear([contents:armi,        contents:coup], 2, false)̂0.4 using passage search method:        CONTEXT

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

FIG. 1 depicts a schematic diagram of one illustrative embodiment of aquestion/answer creation (QA) system 100 in a computer network 102. QAsystem 100 may include a knowledge manager computing device 104(comprising one or more processors and one or more memories, andpotentially any other computing device elements generally known in theart including buses, storage devices, communication interfaces, and thelike) that connects QA system 100 to the computer network 102. Thenetwork 102 may include multiple computing devices 104 in communicationwith each other and with other devices or components via one or morewired and/or wireless data communication links, where each communicationlink may comprise one or more of wires, routers, switches, transmitters,receivers, or the like. QA system 100 and network 102 may enablequestion/answer (QA) generation functionality for one or more contentusers. Other embodiments of QA system 100 may be used with components,systems, sub-systems, and/or devices other than those that are depictedherein.

QA system 100 may be configured to receive inputs from various sources.For example, QA system 100 may receive input from the network 102, acorpus of electronic documents 107 or other data, a content creator,content users, and other possible sources of input. In one embodiment,some or all of the inputs to QA system 100 may be routed through thenetwork 102. The various computing devices on the network 102 mayinclude access points for content creators and content users. Some ofthe computing devices may include devices for a database storing thecorpus of data. The network 102 may include local network connectionsand remote connections in various embodiments, such that knowledgemanager 100 may operate in environments of any size, including local andglobal, e.g., the Internet. Additionally, knowledge manager 100 servesas a front-end system that can make available a variety of knowledgeextracted from or represented in documents, network-accessible sourcesand/or structured data sources. In this manner, some processes populatethe knowledge manager with the knowledge manager also including inputinterfaces to receive knowledge requests and respond accordingly.

In one embodiment, the content creator creates content in electronicdocuments 107 for use as part of a corpus of data with QA system 100.Electronic documents 107 may include any file, text, article, or sourceof data for use in QA system 100. Content users may access QA system 100via a network connection or an Internet connection to the network 102,and may input questions to QA system 100 that may be answered by thecontent in the corpus of data. As further described below, when aprocess evaluates a given section of a document for semantic content,the process can use a variety of conventions to query it from theknowledge manager. One convention is to send a well-formed question.Semantic content is content based on the relation between signifiers,such as words, phrases, signs, and symbols, and what they stand for,their denotation, or connotation. In other words, semantic content iscontent that interprets an expression, such as by using Natural Language(NL) Processing. Semantic data 108 is stored as part of the knowledgebase 106. In one embodiment, the process sends well-formed questions(e.g., natural language questions, etc.) to the knowledge manager. QAsystem 100 may interpret the question and provide a response to thecontent user containing one or more answers to the question. In someembodiments, QA system 100 may provide a response to users in a rankedlist of answers.

The QA system may receive an input question which it then parses toextract the major features of the question, that in turn are then usedto formulate queries that are applied to the corpus of data. Based onthe application of the queries to the corpus of data, a set ofhypotheses, or candidate answers to the input question, are generated bylooking across the corpus of data for portions of the corpus of datathat have some potential for containing a valuable response to the inputquestion.

The QA system then performs deep analysis on the language of the inputquestion and the language used in each of the portions of the corpus ofdata found during the application of the queries using a variety ofreasoning algorithms. There may be hundreds or even thousands ofreasoning algorithms applied, each of which performs different analysis,e.g., comparisons, and generates a score. For example, some reasoningalgorithms may look at the matching of terms and synonyms within thelanguage of the input question and the found portions of the corpus ofdata. Other reasoning algorithms may look at temporal or spatialfeatures in the language, while others may evaluate the source of theportion of the corpus of data and evaluate its veracity.

The scores obtained from the various reasoning algorithms indicate theextent to which the potential response is inferred by the input questionbased on the specific area of focus of that reasoning algorithm. Eachresulting score is then weighted against a statistical model. Thestatistical model captures how well the reasoning algorithm performed atestablishing the inference between two similar passages for a particulardomain during the training period of the QA system. The statisticalmodel may then be used to summarize a level of confidence that the QAsystem has regarding the evidence that the potential response, i.e.candidate answer, is inferred by the question. This process may berepeated for each of the candidate answers until the QA systemidentifies candidate answers that surface as being significantlystronger than others and thus, generates a final answer, or ranked setof answers, for the input question.

Types of information handling systems that can utilize QA system 100range from small handheld devices, such as handheld computer/mobiletelephone 110 to large mainframe systems, such as mainframe computer170. Examples of handheld computer 110 include personal digitalassistants (PDAs), personal entertainment devices, such as MP3 players,portable televisions, and compact disc players. Other examples ofinformation handling systems include pen, or tablet, computer 120,laptop, or notebook, computer 130, personal computer system 150, andserver 160. As shown, the various information handling systems can benetworked together using computer network 102. Types of computer network102 that can be used to interconnect the various information handlingsystems include Local Area Networks (LANs), Wireless Local Area Networks(WLANs), the Internet, the Public Switched Telephone Network (PSTN),other wireless networks, and any other network topology that can be usedto interconnect the information handling systems. Many of theinformation handling systems include nonvolatile data stores, such ashard drives and/or nonvolatile memory. Some of the information handlingsystems shown in FIG. 1 depicts separate nonvolatile data stores (server160 utilizes nonvolatile data store 165, and mainframe computer 170utilizes nonvolatile data store 175. The nonvolatile data store can be acomponent that is external to the various information handling systemsor can be internal to one of the information handling systems. Anillustrative example of an information handling system showing anexemplary processor and various components commonly accessed by theprocessor is shown in FIG. 2.

FIG. 2 illustrates information handling system 200, more particularly, aprocessor and common components, which is a simplified example of acomputer system capable of performing the computing operations describedherein. Information handling system 200 includes one or more processors210 coupled to processor interface bus 212. Processor interface bus 212connects processors 210 to Northbridge 215, which is also known as theMemory Controller Hub (MCH). Northbridge 215 connects to system memory220 and provides a means for processor(s) 210 to access the systemmemory. Graphics controller 225 also connects to Northbridge 215. In oneembodiment, PCI Express bus 218 connects Northbridge 215 to graphicscontroller 225. Graphics controller 225 connects to display device 230,such as a computer monitor.

Northbridge 215 and Southbridge 235 connect to each other using bus 219.In one embodiment, the bus is a Direct Media Interface (DMI) bus thattransfers data at high speeds in each direction between Northbridge 215and Southbridge 235. In another embodiment, a Peripheral ComponentInterconnect (PCI) bus connects the Northbridge and the Southbridge.Southbridge 235, also known as the I/O Controller Hub (ICH) is a chipthat generally implements capabilities that operate at slower speedsthan the capabilities provided by the Northbridge. Southbridge 235typically provides various busses used to connect various components.These busses include, for example, PCI and PCI Express busses, an ISAbus, a System Management Bus (SMBus or SMB), and/or a Low Pin Count(LPC) bus. The LPC bus often connects low-bandwidth devices, such asboot ROM 296 and “legacy” I/O devices (using a “super I/O” chip). The“legacy” I/O devices (298) can include, for example, serial and parallelports, keyboard, mouse, and/or a floppy disk controller. The LPC busalso connects Southbridge 235 to Trusted Platform Module (TPM) 295.Other components often included in Southbridge 235 include a DirectMemory Access (DMA) controller, a Programmable Interrupt Controller(PIC), and a storage device controller, which connects Southbridge 235to nonvolatile storage device 285, such as a hard disk drive, using bus284.

ExpressCard 255 is a slot that connects hot-pluggable devices to theinformation handling system. ExpressCard 255 supports both PCI Expressand USB connectivity as it connects to Southbridge 235 using both theUniversal Serial Bus (USB) the PCI Express bus. Southbridge 235 includesUSB Controller 240 that provides USB connectivity to devices thatconnect to the USB. These devices include webcam (camera) 250, infrared(IR) receiver 248, keyboard and trackpad 244, and Bluetooth device 246,which provides for wireless personal area networks (PANs). USBController 240 also provides USB connectivity to other miscellaneous USBconnected devices 242, such as a mouse, removable nonvolatile storagedevice 245, modems, network cards, ISDN connectors, fax, printers, USBhubs, and many other types of USB connected devices. While removablenonvolatile storage device 245 is shown as a USB-connected device,removable nonvolatile storage device 245 could be connected using adifferent interface, such as a Firewire interface, etcetera.

Wireless Local Area Network (LAN) device 275 connects to Southbridge 235via the PCI or PCI Express bus 272. LAN device 275 typically implementsone of the IEEE .802.11 standards of over-the-air modulation techniquesthat all use the same protocol to wireless communicate betweeninformation handling system 200 and another computer system or device.Optical storage device 290 connects to Southbridge 235 using Serial ATA(SATA) bus 288. Serial ATA adapters and devices communicate over ahigh-speed serial link. The Serial ATA bus also connects Southbridge 235to other forms of storage devices, such as hard disk drives. Audiocircuitry 260, such as a sound card, connects to Southbridge 235 via bus258. Audio circuitry 260 also provides functionality such as audioline-in and optical digital audio in port 262, optical digital outputand headphone jack 264, internal speakers 266, and internal microphone268. Ethernet controller 270 connects to Southbridge 235 using a bus,such as the PCI or PCI Express bus. Ethernet controller 270 connectsinformation handling system 200 to a computer network, such as a LocalArea Network (LAN), the Internet, and other public and private computernetworks.

While FIG. 2 shows one information handling system, an informationhandling system may take many forms, some of which are shown in FIG. 1.For example, an information handling system may take the form of adesktop, server, portable, laptop, notebook, or other form factorcomputer or data processing system. In addition, an information handlingsystem may take other form factors such as a personal digital assistant(PDA), a gaming device, ATM machine, a portable telephone device, acommunication device or other devices that include a processor andmemory.

FIG. 3 is a high level diagram that depicts enhanced weighting andinclusion of search terms. A question answering (QA) system utilizespipeline 300 to process a given question, often posed using naturallanguage, to ultimately provide one or more responsive answers to thequestion. QA system pipeline 300 is comprised of a number of phases. Oneof the initial phases receives the search request from the requestor,such as an end user, with this search request being stored in memoryarea 310. Another phase in QA system pipeline 300 is search phase 320during which a search is formulated with such formulated search beingprocessed by the QA system against a knowledge base, or corpus, that ismanaged by the QA system. The approach described herein is animprovement to search phase 320 of QA system pipeline 300. Inparticular, the approach provides enhanced weighting and inclusion ofsearch terms. Enhanced weighting of search terms (process 330) utilizesthe algorithm shown in process 330 to provide enhanced weighting ofsearch terms which can include unigrams (single words found in thesearch request), bigrams (two words found adjacent to one another in thesearch request), trigrams (three words found adjacent to one another inthe search request, and so on.

The approach processes n-gram models using the algorithm shown below,where W=the weight of the term, n=the number of grams, α_(i)=constantvalue for gram (i), and L_(i)=the likelihood of the term (likelihood ofsingle word for unigram, two adjacent words for bigram, etc.).

$W = {\sum\limits_{i = 1}^{n}\; {\alpha_{i}*{{abs}\left( L_{i} \right)}}}$

For any given corpus, the constants to use can be determined by trainingnd testing based on the documents in the corpus (document database).

Search term inclusion process 350 provides two thresholds that are used(t₁ and t₂) so that if a term exceeds (is greater than) the firstthreshold (t₁) then the approach ensures that the term is not removed bya stop list (e.g., list of words commonly removed from a search, etc.).If the term exceeds the second threshold (t₂), then the approach ensuresthat the term is included as a mandatory term in the search.

The idea behind this approach is if unlikely words are in a question(relative to works preceding them), they may be particular relevant andboosted in a variety of ways. The weights are calculated using theformula above based on log likelihood. These weights are added to theLucene query. The resulting weighted and expanded search terms arestored in memory area 340 and are used by the QA system in further QAsystem pipeline phases to search documents and passages maintained bythe QA system.

FIG. 4 is a diagram showing a first example of a comparison of weightedquery terms using traditional weighting and inclusion of search termsand query terms boosted with enhanced weighting and inclusion of searchterms. In this first example, question 400 is being posed “Who didPakistan's Supreme Court acquit of hijacking charges dating from an 1999army coup?” The unigram (single word) terms in the search are shown inbox 410. For comparison purposes, the words are shown being processed byboth the traditional approach (process 425) as well as by the enhancedweighting and inclusion of search terms process 325. Box 430 shows thequery terms, in this case unigrams, all having equal weights as is theresult of traditional approaches that do not utilize enhanced weightingand inclusion of search terms. Note that the weights pertaining to eachof the words in box 430 is the same value (1.0). In contrast, box 450shows the same terms with boosted weights that result from enhancedweighting process 325. The queries resulting from query terms 430 and450, respectively, also differ due to the enhanced weighting that wasprovided with process 325 instead of equal weighting process 425.

Passages returned by queries using the respective query terms, in theexample, show that only three passages with correct answers werereturned using the traditional approach (ranked passages 1, 2, and 10)as depicted in box 440, while the query with boosted weights resultingin six passages with correct answers (ranked passages 1, 2, 3, 4, 7, and10) as depicted in box 460. In other words, if the correct answer isactually in one of the passages not returned by the traditional ranking(e.g., ranked passages 3, 4, or 7), then the traditional approach wouldnot have the correct answer to pass to final merger ranking process 470,while the process described herein using enhanced weighting would returnthese three passages to final merger ranking process 470.

FIG. 5 is a diagram showing a second example of a comparison of weightedquery terms using traditional weighting and inclusion of search termsand query terms boosted with enhanced weighting and inclusion of searchterms. In this first example, question 500 is being posed “The dominantPalestinian political groups are Fatah in the West Bank & Hamas in whatterritory?” The unigram (single word) terms in the search are shown inbox 510. For comparison purposes, the words are shown being processed byboth the traditional approach (process 425) as well as by the enhancedweighting and inclusion of search terms process 325. Box 530 shows thequery terms, in this case unigrams, all having equal weights as is theresult of traditional approaches that do not utilize enhanced weightingand inclusion of search terms. Note that the weights pertaining to eachof the words in box 530 is the same value (1.0). In contrast, box 550shows the same terms with boosted weights that result from enhancedweighting process 325. The queries resulting from query terms 530 and550, respectively, also differ due to the enhanced weighting that wasprovided with process 325 instead of equal weighting process 425.

Passages returned by queries using the respective query terms, in theexample, show that five passages with correct answers were returnedusing the traditional approach (ranked passages 2, 3, 5, 8, and 10) asdepicted in box 540, while the query with boosted weights resulting insix assages with correct answers (ranked passages 1, 2, 5, 6, 7, and 8)as depicted in box 560. While some of the ranked passages returned witheach approach overlap (2, 5, and 8), the traditional approach appears tohave returned an extraneous passage (passage 10), while not includingrelevant ranked passages 1 and 6 that were returned using the enhancedweighting of terms provided by process 325. In other words, if thecorrect answer is actually in one of the passages not returned by thetraditional ranking (e.g., ranked passages 1 or 6), then the traditionalapproach would not have the correct answer to pass to final mergerranking process 570, while the process described herein using enhancedweighting would return these three passages to final merger rankingprocess 570. In addition, ranked passage 10 (included by equal weightingapproach 425 but not enhanced weighting process 325) might havemisleading information that could result in the equal weighting processreturning an incorrect answer if passage 10 is relied upon during finalmerger ranking process 570.

FIG. 6 is a depiction of a search weight calculation of terms includedin a third example question posed to a QA system using enhancedweighting and inclusion of search terms. In contrast to the examplesshown in FIGS. 4 and 5, FIG. 6 is also depicting bigram search terms,which are the sets of adjacent words found in the question.

In this example, question 600 is posed to the QA system with thequestion being, “In September 2011, Iran released how many Americanhikers who were imprisoned on charges of espionage?” Enhanced weightingand inclusion of search terms process 325 process the question resultingin the data shown in table 605.

Table 605 is shown with five columns of data—unigram, or word, data incolumn 610 which is each word individually. Log likelihood column 620depicts the likelihood of the corresponding unigram (word) occurringwith such values being retrieved from a separate data store of loglikelihood values. Bigrams, which are sets of two adjacent words, areshown in column 630 with the respective log likelihoods of such bigramsbeing depicted in column 640. Finally, search weight calculation 650processes the data shown in the respective row using the aforementionedalgorithm which is reproduced below:

$W = {\sum\limits_{i = 1}^{n}\; {\alpha_{i}*{{abs}\left( L_{i} \right)}}}$

The constants used in the equation above for the corpus being processedare α₁ (constant for unigrams) being set to 0.5, and α₂ (constant forbigrams) being set to 0.3. The resulting search weight calculationsusing the above algorithm and constants for the respective terms in eachrow are shown in column 650.

FIG. 7 is a depiction of a flowchart showing the logic used to computeenhanced weighting and inclusion of search terms for a given search.FIG. 7 processing commences at 700 and shows the steps taken by aprocess that calculates enhanced weighting and inclusion of search termsfound in a given question. At step 710, the process retrieves theconstant values for the given application (e.g., corpus, etc.) to usefor each of the “n-grams” (e.g., unigrams, bigrams, trigrams, etc.). Theconstants used for the various grams are retrieved from data store 720.At step 725, the process initializes the current n-gram level to(unigram). At step 730, the process retrieves the constant to use forcurrent gram level (e.g., unigram=0.5, bigram=0.3, etc.).

At step 740, the process selects the first search term from data store750 (e.g., example column 610 for unigram terms and 630 for bigram termsfrom table 605 depicted in FIG. 6). At step 755, the process retrieveslog likelihood value (L) for selected search term in current gram level(unigram, bigram, etc.) from data store 760. For example, the loglikelihood values depicted in example columns 620 for unigram likelihoodvalues and 640 for bigram likelihood values from table 605 depicted inFIG. 6). At step 765, the process calculates weight of search term atcurrent gram level (W=a * abs(L)) and adds the result to the currentweight of this term which is stored in memory area 770. For example, thecalculation results depicted in example column 650 from table 605depicted in FIG. 6). The process determines as to whether there are moresearch terms that need to be processed for the current n-gram level(decision 775). If there are more search terms that need to be processedfor the current n-gram level, then decision 775 branches to the ‘yes’branch which loops back to step 740 to select and process the nextsearch term as described above. This looping continues until all of thesearch terms have been processed for the current n-gram level, at whichpoint decision 775 branches to the ‘no’ branch exiting the loop.

The process next determines whether there are more gram levels toprocess (decision 780). For example, if both unigrams and bigrams arebeing processed and processing has completed the unigram processing(1-gram), then processing would loop in order to process the bigrams(2-grams). If there are more gram levels to process, then decision 780branches to the ‘yes’ branch which branches to step 785 to increment thecurrent gram level (e.g., to bigrams, trigrams, etc.) and also sets thesearch term selection to first search term before loops back to step 730to process the search terms using the newly set gram level. This loopingcontinues until all of the gram levels have been processed, at whichpoint decision 780 branches to the ‘no’ branch exiting the loop. Atpredefined process 790, the process performs the Inclusion of SearchTerms and Perform Search Using Weighted/Expanded Search Terms routine(see FIG. 8 and corresponding text for processing details). The searchresults are returned by predefined process 790 and stored in memory area795. FIG. 7 processing thereafter ends at 799.

FIG. 8 is a depiction of a flowchart showing the logic used to expandsearch terms used in query based on enhanced weighting and inclusion ofsearch terms. FIG. 8 processing commences at 800 and shows the stepstaken by a process that includes (expands) search terms based onenhanced weighting applied to the search terms and also perform a searchof the corpus using the weighted and expanded search terms. At step 810,the process retrieves a first threshold (t₁) that is used in comparingto search term weights to keep search terms off of the removal list anda second threshold (t₂) that is used in comparing to such search termsto make certain terms mandatory search terms in the eventual search. Thefirst and second threshold values are retrieved from data store 820.

At step 825, the process selects the first search term and itscorresponding weight from memory area 770. The process then determineswhether the selected search term's weight is greater than the firstthreshold value (decision 830). If the selected search term's weight isgreater than the first threshold value, then decision 830 branches tothe ‘yes’ branch to further evaluate the search term's weight. On theother hand, if the selected search term's weight is not greater than thefirst threshold value, then decision 830 branches to the ‘no’ branchbypassing the remaining search term evaluation steps. The process nextdetermines whether the selected search term's weight is greater than thesecond threshold (decision 840). If the selected search term's weight isgreater than the second threshold, then decision 840 branches to the‘yes’ branch whereupon, at step 845, the process adds the selectedsearch term to a list of mandatory search terms that are stored inmemory area 850. On the other hand, if the selected search term's weightis less than or equal to the second threshold (but still greater thanthe first threshold), then decision 840 branches to the ‘no’ branchwhereupon, at step 855 the process keeps, or inhibits, the selectedsearch term from being added to a list of terms not included in (removedfrom) the search by adding the selected term to memory area 860. Theprocess determines as to whether there are more search terms to selectand process as described above (decision 865). If there are more searchterms to select and process, then decision 865 branches to the ‘yes’branch which loops back to step 825 to select and process the nextsearch term using the next search term's weight value. This loopingcontinues until all of the search terms have been processed, at whichpoint decision 865 branches to the ‘no’ branch exiting the loop.

At step 870, the process prepares the document and passage queries usingboth the enhanced weighting of the search terms as well as the enhancedinclusion of search terms as provided by steps 825 through 865. Queriesusing weighted and expanded search terms 875 include document query 880as well as passage query 885. At step 890, the process searches theknowledge base (corpus 106) using the prepared passage query 880 anddocument query 885. The results of the search are stored in memory area795, where they can be provided to the requestor, such as an end user oranother process that requested the search. FIG. 8 processing thereafterreturns to the calling routine (see FIG. 7) at 895.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, that changes and modifications may bemade without departing from this invention and its broader aspects.Therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. It will be understood by those with skill in the artthat if a specific number of an introduced claim element is intended,such intent will be explicitly recited in the claim, and in the absenceof such recitation no such limitation is present. For non-limitingexample, as an aid to understanding, the following appended claimscontain usage of the introductory phrases “at least one” and “one ormore” to introduce claim elements. However, the use of such phrasesshould not be construed to imply that the introduction of a claimelement by the indefinite articles “a” or “an” limits any particularclaim containing such introduced claim element to inventions containingonly one such element, even when the same claim includes theintroductory phrases “one or more” or “at least one” and indefinitearticles such as “a” or “an”; the same holds true for the use in theclaims of definite articles.

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 8. An information handling system comprising: one or more processors; a memory coupled to at least one of the processors; and a set of computer program instructions stored in the memory and executed by at least one of the processors in order to perform actions comprising: receiving a question at a question answering (QA) system that includes a plurality of words; calculating a plurality of weights that correspond to a plurality of search terms included in the plurality of words, wherein the search terms include the plurality of words; generating a query based on the question and the calculated plurality of weights; and searching, using the generated query, a corpus managed by the QA system, wherein the searching results in one or more search results.
 9. The information handling system of claim 8 wherein the actions further comprise: comparing the calculated weight corresponding to a selected one of the search terms to a threshold; and in response to the selected search term's calculated weight meeting the threshold, inhibiting removal of the selected search term from the generated query.
 10. The information handling system of claim 8 wherein the actions further comprise: comparing the calculated weight corresponding to a selected one of the search terms to a threshold; and in response to the selected search term's calculated weight meeting the threshold, adding the selected search term to a list of mandatory search terms included in the generated query.
 11. The information handling system of claim 8 wherein the actions further comprise: retrieving a unigram constant value; retrieving a likelihood value corresponding to each of the plurality of words; and calculating a unigram weight corresponding to each of the plurality of words based on the unigram constant value and each of the plurality of words' likelihood values, wherein the unigram weight is included in the plurality of weights.
 12. The information handling system of claim 11 wherein the calculating further comprises: multiplying the unigram constant by an absolute value of each of the plurality of words' likelihood values.
 13. The information handling system of claim 8 wherein the actions further comprise: retrieving a bigram constant value; retrieving a likelihood value corresponding to each of a plurality of bigrams included in the plurality of words; and calculating a bigram weight corresponding to each of the plurality of bigrams based on the bigram constant value and each of the plurality of bigrams' likelihood values, wherein the bigram weight is included in the plurality of weights.
 14. The information handling system of claim 8 wherein the actions further comprise: identifying a number of grams, wherein each of the grams have a constant value and a set of likelihood values, and wherein the grams include at least a single gram (unigram) and a double gram (bigram); for each of the identified number of grams: selecting each of the search terms based on the current number of grams; and calculating the weight of each of the search terms by multiplying the constant corresponding to the current number of grams by the likelihood value of the selected search term from the set of likelihood values pertaining to the current number of grams.
 15. A computer program product stored in a computer readable storage medium, comprising computer program code that, when executed by an information handling system, performs actions comprising: receiving a question at a question answering (QA) system that includes a plurality of words; calculating a plurality of weights that correspond to a plurality of search terms included in the plurality of words, wherein the search terms include the plurality of words; generating a query based on the question and the calculated plurality of weights; and searching, using the generated query, a corpus managed by the QA system, wherein the searching results in one or more search results.
 16. The computer program product of claim 15 wherein the actions further comprise: comparing the calculated weight corresponding to a selected one of the search terms to a threshold; and in response to the selected search term's calculated weight meeting the threshold, inhibiting removal of the selected search term from the generated query.
 17. The computer program product of claim 15 wherein the actions further comprise: comparing the calculated weight corresponding to a selected one of the search terms to a threshold; and in response to the selected search term's calculated weight meeting the threshold, adding the selected search term to a list of mandatory search terms included in the generated query.
 18. The computer program product of claim 15 wherein the actions further comprise: retrieving a unigram constant value; retrieving a likelihood value corresponding to each of the plurality of words; and calculating a unigram weight corresponding to each of the plurality of words based on the unigram constant value and each of the plurality of words' likelihood values, wherein the unigram weight is included in the plurality of weights.
 19. The computer program product of claim 15 wherein the actions further comprise: retrieving a bigram constant value; retrieving a likelihood value corresponding to each of a plurality of bigrams included in the plurality of words; and calculating a bigram weight corresponding to each of the plurality of bigrams based on the bigram constant value and each of the plurality of bigrams' likelihood values, wherein the bigram weight is included in the plurality of weights.
 20. The computer program product of claim 15 wherein the actions further comprise: identifying a number of grams, wherein each of the grams have a constant value and a set of likelihood values, and wherein the grams include at least a single gram (unigram) and a double gram (bigram); for each of the identified number of grams: selecting each of the search terms based on the current number of grams; and calculating the weight of each of the search terms by multiplying the constant corresponding to the current number of grams by the likelihood value of the selected search term from the set of likelihood values pertaining to the current number of grams. 